Mammalian Ovulation is a complex process involving rupture of a mature follicle and extra sion of the oocyte. As follicles mature they swell; follicular fluid is a transudate of follicular blood vessels. Swelling of the follicle causes thinning of the apical follicle wall. Rupture occurs at the apex of the follicle where collagen fibers have become less abundant. Theories have proposed that either the release of hydrolytic enzymes or the development of an inflammatory condition is responsible for the loss of collagen fibers from the follicle apex. However, in either case it is not clear whether the collagen fibers themselves or the matrix cementing them into bundles is being effected. The proposed research on mammalian ovulation deals with the role of the microvasculature in swelling of the follicle and the effect of swelling on the structure of the follicle wall. This work has 3 objectives. First, to study the morphology and development of follicle microvasculature by examining corrosion casts with scanning electron microscopy. The complexity of this important system has evaded attempts to study it by serial section reconstruction. The microvasculature provides fluid for follicle swelling, nutrients for follicle growth and hormonal cues to regulate maturational processes. Disruption of the microvasculature may lead to atresia or necrosis at the follicle apex and ovulation. The second objective is to explain how follicle swelling causes thinning of the follicle wall; does thinning involve cell death, migration and/or stretching? Careful measurements of cell dimension correlated with measurements of follicle diameter and wall thickness will resolve this question. The third objective is to determine how the layer of collagen fibers surrounding mature follicles is altered to allow for follicle rupture. We have developed a technique for removing tissue superficial to the collagen fibers thereby permitting direct observation of changes in this layer by scanning electron microscopy. The work outlined in this proposal employs new methods of studying the mechanisms involved in ovulation and in particular will help clarify the role of follicle swelling, the microvasculature and the collagen fibers in this process.